This invention relates to method and system for controlling an internal combustion engine provided with electromagnetically actuated intake and exhaust valves, and more particularly to the controlling method and system which can suppress variation in engine speed under idling engine operation.
Hitherto a control technique for stabilizing idling engine speed in an internal combustion engine provided with electromagnetically actuated intake and exhaust valves has been proposed in Japanese Patent Provisional Publication No. 10-37787. According to this conventional control technique, a control system includes an intake and exhaust valve opening and closing timing changing means for changing at least one of the opening and closing timings of each intake and exhaust valves, for the purpose of regulating the idling engine speed. Additionally, in such a conventional internal combustion engine provided with electromagnetically actuated intake and exhaust valves, at least two kinds of crank angle sensor signals are used for detecting engine speed and standard position for each cylinder, for the purpose of setting control timings. They are a position (POS) signal representative of a certain rotational angle of a crankshaft, and a reference (REF) signal or cylinder synchronous signal representative of the standard position in an operating cycle of each cylinder. The position signal is generated, for example, every 1 degree of the crank angle.
In the conventional control technique on the assumption that a Ref signal (pulse) represents the intake stroke for a specified cylinder, the opening and closing timings of the intake valve for this cylinder are calculated and set at the timing in synchronism with a Ref signal which is generated two or three Ref signals before the Ref signal representative of the intake stroke for the specified cylinder. Here, the reason why the calculation and setting are made in synchronism with such a considerably preceding Ref signal and not in synchronism with the immediately preceding Ref signal is to ensure a certain software prosecution time even in a high engine speed operating range where the interval between the adjacent Ref signals is relatively short, in the control system in which the calculating and setting of the opening and closing timings of the intake valve is usually carried out using a software in a microprocessor as an electronic control unit.
Drawbacks have been encountered in the above conventional control technique, in which the opening and closing timing of the intake valve are calculated and set always in synchronism with the Ref signal generated two or three Ref signals before the Ref signal representative of the intake stroke for the specified cylinder, regardless of engine speed of the conventional engine provided with the electromagnetically actuated intake and exhaust valves. Accordingly, in a low engine speed operating range such as idling, a considerable time has lapsed from calculation and setting of the opening and closing timing of the intake valve to actual opening and closing of this intake valve to suck air into the cylinder, so that engine speed may be lowered during this considerable time. However, such a lowered engine speed cannot be corrected, and therefore stability of engine revolution is degraded in the low engine speed operating range, particularly at idling.
In addition, in the engine provided with the electromagnetically actuated intake valves, each intake valve is operated to open and close at the previously set opening and closing timings. Accordingly, when the engine speed is lowered, the opening and closing time durations of the intake valve are relatively shortened to movement of the piston, as compared with a conventional internal combustion engine provided with cam-operated intake valves and arranged such that the opening and closing time durations of the intake valve are momentarily increased or decreased under the action of the cam operated in synchronism with the piston. Thus, in the engine provided with the electromagnetically actuated intake valves, the amount of intake air to be sucked into the cylinder is further lowered thereby further lowering the engine speed.
Therefore, it is an object of the present invention to provide improved method and system for controlling an internal combustion engine provided with electromagnetically actuated engine valves, which can effectively overcome drawbacks encountered in conventional controlling methods and systems for an internal combustion engine of the same type.
Another object of the present invention is to provide an improved method and system for controlling an internal combustion engine provided with electromagnetically actuated engine valves, which can effectively suppress an engine speed variation during a low engine speed operation such as idling, thereby achieving stable idling operation of the engine.
A first aspect of the present invention resides in a method of controlling an internal combustion engine having an electromagnetically actuated intake valve for a cylinder, comprising: (a) forming first and second control regions in accordance with an engine speed of the engine, the first control region being higher in engine speed than the second control region; (b) calculating opening and closing timings of the intake valve in synchronism with (at a timing synchronized with) a first cylinder synchronous signal in the first control region, the first cylinder synchronous signal being generated in synchronism with a stroke of an operating cycle of a cylinder; (c) calculating the opening and closing timings of the intake. valve in synchronism with a second cylinder synchronous signal in the second control region, the second cylinder synchronous signal being generated in synchronism with the stroke of the operating cycle of a cylinder and after generation of the first cylinder synchronous signal; and (d) controlling an amount of intake air to be supplied to the cylinder in accordance with the calculated opening timing of the intake valve.
A second aspect of the present invention resides in a method of controlling an internal combustion engine having first, second and third cylinders whose operating cycles are carried out in the sequence set forth, the third cylinder being provided with an electromagnetically actuated intake valve, the method comprising: (a) forming first and second control regions in accordance with an engine speed of the engine, the first control region being higher in engine speed than the second control region; (b) calculating opening and closing timings of the intake valve in synchronism with a first cylinder synchronous signal in the first control region, the first cylinder synchronous signal being generated in synchronism with a stroke of an operating cycle of the first cylinder and before the stroke of the operating cycle of the third cylinder; (c)calculating the opening and closing timings of the intake valve in synchronism with a second cylinder synchronous signal in the second control region, the second cylinder synchronous signal being generated in synchronism with the stroke of the operating cycle of the second cylinder and after generation of the first synchronous signal, the second cylinder synchronous signal being generated before the stroke of the operating cycle of the third cylinder; and (d) controlling an amount of intake air to be supplied to the cylinder in accordance with the calculated opening timing of the intake valve.
A third aspect of the present invention resides in a method of controlling an internal combustion engine having an electromagnetically actuated intake valve for a cylinder, comprising: (a) calculating opening and closing timings of the intake valve in synchronism with a first cylinder synchronous signal which is generated in synchronism with a stroke of an operating cycle of a cylinder; and (b) again calculating at least the closing timing of the intake valve in synchronism with a second cylinder synchronous signal when an idling engine speed is lowered after generation of the first cylinder synchronous signal so as to maintain the idling engine speed at a predetermined level, the second cylinder synchronous signal being generated in synchronism with the stroke of the operating cycle of a cylinder and after generation of the first cylinder synchronous signal.
A fourth aspect of the present invention resides in a method of controlling an internal combustion engine having an electromagnetically actuated intake valve for a cylinder, comprising: (a) providing an electromagnetic actuator having an opening-side electromagnet which causes the intake valve to open upon flowing current therethrough and close upon interruption of the current; and (b) causing current to flow through the opening-side electromagnet of the electromagnetic actuator after interruption of flow of the current to the opening-side electromagnet, when an engine speed of the engine is lowered after a closing timing of the intake valve is set.
A fifth aspect of the present invention resides in a control system for an internal combustion engine having an electromagnetically actuated intake valve for a first cylinder. The control system comprises an engine speed sensor for detecting an engine speed of the engine, and a cylinder synchronous signal sensor for detecting cylinder synchronous signals which correspond to predetermined timings of operating cycles of the first cylinder and other cylinders, respectively. Additionally, a control unit is provided to be configured to perform (a) determining a plurality of control regions in accordance with the engine speed detected by the engine speed sensor, and (b)calculating and setting opening and closing timings of the intake valve for the first cylinder, in synchronism with different cylinder synchronous signals respectively in the different control regions.